The present invention relates generally to engine noise rejection and more particularly, to a system for rejecting noise in engine ignition knock data.
Premature detonation, pre-ignition, or combustion knock, occurs in internal combustion engines when the air/fuel mixture is being compressed by the engine cylinder and the compression temperature causes auto-ignition of the air/fuel mixture prior to ignition of the spark plug for that cylinder. Combustion knock can also occur when some or all of the air fuel mixture in the combustion chamber auto-ignites, or detonates, due to excessive in-cylinder compression temperature.
Premature detonation or knocking can cause severe damage to an engine as the pressure wave from the knock can destroy the cylinder thermal boundary layer, causing the cylinder and piston to reach temperatures near the actual temperature of combustion. In an engine, this elevated temperature, combined with the pressure wave from the knock, can adversely affect the piston crown, which has a melting point much lower than the temperature of combustion. Even in engines with steel cylinder liners that can withstand the elevated temperatures, the piston rings in contact with the liners can be adversely affected by the elevated temperatures and may fail. Allowing an engine to operate under a knocking condition can therefore possibly lead to severe engine damage.
The detection of knocking is thus of significant interest in regulating the mixture composition and/or the instant of ignition. Detecting knocking with the aid of torque meters, acceleration meters or microphones is already known. However, such methods require frequency filters that permit the passage of a frequency that is specific for knocking. Knocking cannot be extracted as a pure signal in this manner, but only as a derived signal.
The detection of knocking with the aid of an ionic current sensor is also known. More specifically, when a spark is produced at the spark plug and the air/fuel mixture burns in the combustion chamber, the air/fuel mixture is ionized. When a voltage is applied to the spark plug while the mixture is in the ionized state, an ion current is generated. The occurrence of knock can be detected by detecting and analyzing this ion current. Usually, when knock occurs, an oscillating component of six kHz to seven kHz appears in the ion current. The knock detection device based on the ion current extracts this frequency component peculiar to knock by means of a filter, and analyzes the knocking condition based on the magnitude of that component.
It has been ascertained that the output signal of the ionic current sensor has low and high frequency components and that the high frequency components increase in uniformity with the intensity of engine knocking. The difficulty has been the separation of the low frequency ionic currents and high frequency noise from the high frequency ionic currents that are specific for knocking. Some of the high frequency noise can be reduced, but there are periodic occurrences of high-energy bursts that cannot be easily filtered out using ordinary electronic filters.
To this end, several practical solutions have been attempted. Typically, the high-energy bursts usually have higher voltage amplitudes then a knock signal. Therefore, one method to discriminate between a valid knock and noise is based upon voltage amplitude. When the ion signal peak amplitude is high, the signal is noise. Unfortunately, not all of the noise bursts have higher amplitudes. This results in having to trade-off how much noise to tolerate versus lowering the threshold and rejecting a certain percentage of true knock events. Another problem with this method is that the voltage threshold needs to vary with different operating conditions, i.e. temperature, humidity, different fuels, age of the engine, etc.
The disadvantages associated with these conventional noise rejection techniques have made it apparent that a new technique for rejecting noise in ignition knock data is needed. Preferably, the new technique would be able to accurately discriminate between ignition knock data and noise. The new technique should also not vary with different operating conditions.
It is, therefore, an object of the invention to provide an improved and reliable means for accurately determining and minimizing noise in ignition knock data. Another object of the invention is to accurately discriminate between ignition knock data and noise.
In one aspect of the invention, a device for rejecting noise in an ion-sense ignition knock signal compares an integrated knock signal to a peak knock signal multiplied by a time factor to determine the presence of noise. A bandpass filter coupled to an engine""s spark plug through ion-sensing circuitry generates a filtered knock signal. The filtered knock signal is passed through a rectifier to produce a rectified knock signal. The rectified knock signal is then passed through an integrator and a peak detector to produce an integrated knock signal and a peak knock signal, respectively. The peak knock signal is multiplied by a predetermined time factor and the result is compared to the integrated knock signal. If the result is less than the integrated knock signal, then a noise disturbance has not occurred and the integrated knock signal is passed on to a knock detector. If, on the other hand, the result is greater than the integrated knock signal, a noise disturbance has occurred and the integrated signal is reduced to some minimum value before being passed on to the knock detector.
The present invention thus achieves an improved and reliable means for rejecting noise in ignition knock data. Also, the present invention is advantageous in that it does not vary with different operating conditions.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.